Solid-bowl centrifuge having a disk stack on the drum cover

ABSTRACT

The present invention is a solid-bowl screw centrifuge that includes a centrifugal drum. The drum has a drum casing and a screw with a screw body that is surrounded by a screw blade. The screw blade forms at least one screw spiral with a conveying path for transporting material to be centrifuged. The centrifuge also includes an inlet into the centrifugal drum, at least one solid matter discharge and at least one liquid outlet. The centrifuge includes a drum chamber that is axially closed by a drum cover having essentially a conical shape. Further included is a disk stack having at least one conical disk, and the disk stack is mounted to the drum cover directly upstream of the liquid outlet. At least a portion of the disk stack is arranged in a cylindrical section of the drum chamber that has an essentially constant diameter. A screw disk is arranged on the screw body between the drum cover and a first screw spiral.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to solid-bowl screw centrifuges.

It is known from the prior art to provide disk arrangements insolid-bowl screw centrifuges.

U.S. Patent Document U.S. Pat. No. 5,310,399 shows disks which arearranged on the screw body, specifically between several spirals of thescrew.

A similar construction is known from German Patent Document DE 26 17692. Also, in this multi-stage decanter arrangement, the disks arearranged on the screw.

In addition, there are constructions in which a type of disk drum isconnected behind the actual decanter drum (see, for example, IT 496 031or SU 385 629).

Additional known combinations of solid-bowl screw centrifuges with diskinserts are known from International Patent Document WO 98/45045, FrenchPatent Document 1 449 064, French Patent Document 2 532 189 and BritishPatent Document GB 998 669.

In British Patent Document GB 998 669, a type of a complete separator isconnected on the output side of the decanter as a constructional unit.As a result, the after clarification of the product preclarified in thedecanter basically takes place in a completely separate seriesconnection of the decanter and the separator.

In the separator with the stack of disks, the concentrate is dischargedon a larger diameter of the nozzles and the clarified phase isdischarged in the center. Outside the stack of disks, a solid matterspace is constructed which is bounded on both sides by conical walls.The outside diameter of this separator, for example, in SU 385 629 or GB998 669, is situated on a larger radius than the outside diameter of thedecanter.

The initially mentioned decanter constructions with integrated diskstacks are distinguished in that the disk stacks are each mounted on thescrew bodies and thus rotate at a differential rotational speed withrespect to the drum casing. This necessarily results in disturbing gaps.Furthermore, no optimal utilization of the space can be accomplished.

From International Patent Document WO 99/52641 (as well as parallel U.S.Patent Document U.S. Pat. No. 6,030,332), it is known to mount a diskstack directly upstream of the liquid outlet, so that it is arranged onthe drum cover. However, in this case, it is problematic that the diskstack essentially fills out the cylindrical area of the centrifuge, sothat, differently than in British Patent Document GB-A-998669, aseparator is not connected to the output side of a complete decanter,which first develops its effect. A similar construction as that of U.S.Patent Document U.S. Pat. No. 6,030,322 is illustrated in German PatentDocument DE 1 482 721.

An aspect of the present invention is a centrifuge that has a dischargeof concentrate take place from an area of a disk stack toward a drumcasing.

The present invention is a solid-bowl screw centrifuge that includes acentrifugal drum. The drum has a drum casing and a screw with a screwbody that is surrounded by a screw blade. The screw blade forms at leastone screw spiral with a conveying path constructed between the at leastone screw spiral for transporting material to be centrifuged. Thecentrifuge also includes an inlet into the centrifugal drum, at leastone solid matter discharge and at least one liquid outlet. Thecentrifuge also includes a drum chamber that is axially closed by a drumcover having essentially a conical shape. Further included is a diskstack having at least one conical disk, and the disk stack is mounted tothe drum cover directly upstream of the liquid outlet. At least aportion of the disk stack is arranged in a cylindrical section of thedrum chamber that has an essentially constant diameter. A screw disk isarranged on the screw body between the drum cover and a first screwspiral of the at least one screw spiral. The screw disk has an interiorsection and a conical exterior section.

The conical section of the screw disk as well as the conical drum coverconstructed opposite the conical section of the screw disk thereby forma solid matter or concentrate collecting space which is conicallytapered twice. That permits a draining of the concentrate toward thedrum casing without requiring a joining of a separately constructedseparator connected to the output side of the decanter. For at leastthis purpose, the disk stack is arranged in a cylindrical section of thedrum chamber with an essentially constant diameter and the disk stack ismounted directly upstream of the liquid outlet, while resting on thedrum cover and/or being arranged on the latter.

Since the stack of disks rests directly on the drum cover or is fastenedthereto, it no longer rotates at a differential rotational speed withrespect to the drum casing but rotates together with it.

In contrast to disk inserts on the screw, a disk insert or stack ofdisks connected with a liquid-side drum casinggenerally preventsdisturbing short-circuit connections from occurring between aclear-phase collecting pipe of the disk stack and a solid matter orconcentrate space outside the disk stack. The concentrate space of thedisk stack is situated on the outside on the disk stack, in which thediameter of the drum casing can be constructed to be continuous orconstant and requires no widening. In this manner, mixtures which aredifficult to clarify, for example, mixtures with fine suspended matter,can be separated.

The maximal radial dimension of the screw disk is preferably smallerthan the radial dimension of the screw blade. In particular, dischargeis achieved by a removal device on the first screw blade whichpenetrates the screw disk.

The drum cover preferably has an essentially conical construction, whichpermits a fastening of the preferably preassembled disk stack on thedrum cover, particularly since the disks of the stack of disks also havea preferably conical construction.

According to an embodiment of the present invention, a clear-phasecollecting pipe is situated at a lower diameter than the exterior wallof the screw body.

The screw disk, located between the first screw spiral, as viewed fromthe drum cover, and the drum coverhas a disk-type interior section and aconical exterior section. The maximal radial dimension of the screw diskis smaller than the radial dimension of the screw blade. The conicalsection of the screw disk as well as the conical drum cover constructedopposite the conical section of the screw disk thereby form the solidmatter or concentrate collecting space which is conically tapered twiceand which permits a draining of the concentrate toward the drum casingby a removal device at the first screw blade which penetrates the screwdisk.

The invention will be better understood and appreciated from thefollowing detailed descriptions and with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a solid-bowl screw centrifuge, accordingto the principles of the present invention.

FIG. 2 is a sectional view of a portion of the solid-bowl screwcentrifuge of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a solid-bowl crew centrifuge having a drive A and a machineframe M. The centrifuge also includes a centrifugal drum 25 with a drumcasing 1 and a screw 2. The screw 2 includes a screw body 3 as well as ascrew blade 4 surrounding the screw body 3 and forming at least onescrew spiral X. Between the at least one screw spiral X, a conveyer pathis constructed for conveying/transporting a material S to becentrifuged.

The screw body 3 has a cylindrical section 5 a, which is slightlystepped in a rearward area (to the right as viewed in FIG. 1), and anadjoining conically tapering section 5 b. The cylindrical section 5 a isaxially closed off by a drum cover 7 which has a conical construction atleast in an area of a drum chamber 6 between the screw body 3 and thedrum casing 1.

The operation of this solid-bowl screw centrifuge is as follows.

The material S to be centrifuged is guided through a centrally arrangedas well as co-rotating inlet pipe 12 by a distributor 20 into the drumchamber 6. As a result of the force of gravity, solid matter particlesdeposit in a very short time on an interior wall of the rotating drumcasing 1. The distributor 20 and the co-rotating inlet pipe 12 form alargely tight system.

The screw 2 rotates at a slightly lower or higher speed than the drum 1and conveys centrifuged solid matter toward the conical section 5 b outof the drum 25 to a solid matter outlet 27.

In contrast, liquid flows toward the cylindrical section 5 a at therearward end of the drum 1 (to the right as viewed in FIG. 1) and isdischarged there via outlet 16 (as shown FIG. 2).

As shown in FIGS. 1 and 2, between first screw spiral X, and drum cover7, a screw disk 8 is arranged on and near an end of the screw body 3.Screw disk 8 has a disk-type interior section 8 a and preferably astabilizing, conical exterior section 8 b. The maximal radial dimensionof the disk 8 is smaller than the radial dimension of the screw blade 4.At the inside diameter of the screw disk 8, at least one opening or ringgap 21 is provided for a passing-through of the liquid.

Between the screw disk 8 and the drum cover 7, a stack 9 of disks 11 isarranged. The stack 9 may be constructed as a unit which can bepreassembled and fastened directly to an interior side of the drum cover7. The stack 9 of disks 11 has a holding device 10 shaped in a manner ofa distributor, which holding device 10 has an interior cylindricalsection 10 a and an axially adjoining conical section 10 b. Between theconical section 10 b and the drum cover 7, the conical disks 11 arearranged and preferably spaced by spacers (not shown) which are adaptedfor a particular application. The spacers may be molded-on strips,punctiform spacers, or equivalent. The conical disks 11 are preferablyconstructed to essentially correspond to the conical shape of the drumcover 7.

In an exterior area of the disks 1, ascending ducts 13 are constructedwhich penetrate the conical section 10 b. As an alternative, the stack 9of disks 11 may be constructed such that a feeding of the material S tobe centrifuged or clarified takes place radially from the outside of thecentrifuge (not shown).

A draining-off of a clear or liquid phase takes place by a collectingpipe 14 at an interior diameter of the disks 11 in a wall of thecylindrical section 10 b.

The collecting pipe 14 is preferably situated at least partially on asmaller diameter, relative to the axis of rotation R, than an exteriorwall of the screw body 3, which results in a more energy-savingoperating mode than an arrangement of the collecting pipe 14 on a largerdiameter of the exterior wall. Such an alternative arrangement, however,is also conceivable. The collecting pipe 14 axially extends into a bore15 of the drum cover 7 which bore 15 leads into a radially outwardextending outlet 16 for discharging the clear or liquid phase.

A concentrate space is situated on an outside area at the stack 9 ofdisks 11, where the diameter of the drum casing 1 has a continuousconstruction and needs no widening. A concentrate discharge takes placeby the screw 2. For discharging solid matter from the concentrate space,the screw 2 has a removal projection 17 which penetrates the disk 8. Thediameter of the drum casing 1 is essentially constant in thisconcentrate space.

For adjusting the liquid level in the drum 25, known systems, such asthe applicant's Varipond System, can be used as shown in German PatentDocument DE 43 20 265. For instance, regulating disk 22 can be slid onaxially adjacent outlet 16. Other adjusting possibilities of the liquidlevel are conceivable, such as a trailing blade disk (not shown)connected behind the disk stack 9.

On the holding device 10 and/or on the drum cover 7, ribs 23 areconstructed on a side facing away (to the left in FIG. 2) from the disks11, which ribs 23 promote introduction of the material S to becentrifuged into the disk stack 9.

An operation of the centrifuge is as follows. The material S to becentrifuged passes through the ring gap 21 and flows along the ribs 23into the ascending ducts 13 of the disk stack 9. Here the clear phase orliquid is drained to the collecting pipe 14 and the solid matter isdischarged to the outside. The solid matter is taken along by theremoval projection 17 and is conveyed by the screw 2 to the conicalsection 5 b.

The disk stack 9 can be cleaned by a flush-back device. As required, acleaning effect can be promoted by an evacuation by a nozzle (not shown)in the outlet 16 or a centrifugal force valve 19.

Spacing between one or more of the disks 11 of the stack 9 is preferablymore than 0.5 mm and less than 3 mm, measured perpendicularly to thesurface of the disks 11. An angle of slope of the conical disks 11 withrespect to the drum axis R is between 35° and 55°, and preferablybetween 40° to 50°.

Preferably, a diameter or maximal radial dimension of the disks 11 at anouter edge amounts to approximately 50 to 75%, and preferably ⅔ of adiameter of a free screw area or radial space between the screw body 3and the drum casing 1, or of a radial space of the drum chamber 6.

Although the present disclosure has been described and illustrated indetail, it is to be clearly understood that this is done by way ofillustration and example only and is not to be taken by way oflimitation. The spirit and scope of the present disclosure are to belimited only by the terms of the appended claims.

1. A solid-bowl screw centrifuge, comprising: a centrifugal drum having a drum casing and a screw, the screw having a screw body surrounded by a screw blade forming at least one screw spiral with a conveying path constructed between the at least one screw spiral for transporting material to be centrifuged; an inlet into the centrifugal drum; at least one solid matter discharge; at least one liquid outlet; a drum chamber axially closed by a drum cover having essentially a conical shape; a disk stack having at least one conical disk, the disk stack being mounted to the drum cover directly upstream of the liquid outlet and at least a portion of the disk stack being arranged in a cylindrical section of the drum chamber that has an essentially constant diameter; and a screw disk arranged on the screw body between the drum cover and a first screw spiral of the at least one screw spiral, the screw disk having an interior section and a conical exterior section.
 2. The solid-bowl screw centrifuge according to claim 1, wherein the conical disks are constructed to essentially correspond to the conical shape of the drum cover.
 3. The solid-bowl screw centrifuge according to claim 1, wherein the disk stack has a collecting pipe for a clarified liquid phase, and the disk stack is at least partially situated closer radially to a rotational axis of the centrifugal drum than an exterior wall of the screw body.
 4. The solid-bowl screw centrifuge according to claim 1, wherein a maximal radial dimension of the screw disk is smaller than a radial dimension of the screw blade.
 5. The solid-bowl screw centrifuge according to claim 1, wherein at least one opening is constructed on an inside diameter of the screw disk for the passing-through of a liquid.
 6. The solid-bowl screw centrifuge according to claim 1, wherein the disk stack is constructed between the screw disk and the drum cover.
 7. The solid-bowl screw centrifuge according to claim 1, wherein the disk stack has a holding device which includes an interior cylindrical section and an axially adjoining conical section, the at least one conical disk being arranged between the axially adjoining conical section and the drum cover.
 8. The solid-bowl screw centrifuge according to claim 7, wherein ascending ducts are constructed in an exterior area of the at least one conical disk, which ascending ducts penetrate the conical section of the holding device.
 9. The solid-bowl screw centrifuge according to claim 7, wherein at least one collecting pipe is constructed in the cylindrical section of the holding device.
 10. The solid-bowl screw centrifuge according to claim 9, wherein the at least one collecting pipe leads into an outlet through a bore of the drum cover.
 11. The solid-bowl screw centrifuge according to claim 1, wherein ribs for introducing the material to be centrifuged into the disk stack are joined to one of the holding device on a side facing away from the at least one conical disk and to the drum cover.
 12. The solid-bowl screw centrifuge according to claim 1, wherein the disk stack is arranged such that the feeding of the material to be centrifuged takes place radially from outside the centrifuge.
 13. The solid-bowl screw centrifuge according to claim 1, wherein the screw has a removal projection for discharging solid matter from a concentrate space.
 14. The solid-bowl screw centrifuge according to claim 1, wherein the inlet is configured such that it rotates along with the screw.
 15. The solid-bowl screw centrifuge according to claim 1, wherein the at least one conical disk includes at least two conical disks and a spacing between each of the at least two conical disks is between approximately 0.5 and 3 mm, as measured perpendicularly to a surface of the at least one conical disk.
 16. The solid-bowl screw centrifuge according to claim 1, wherein an angle of slope of the at least one conical disk, with respect to a rotational axis of the drum, is between 35° and 55°.
 17. The solid-bowl screw centrifuge according to claim 1, wherein a maximal radial dimension of the at least one conical disk is approximately between 50 and 75% of one of a radial space between the screw body and the drum casing and a radial space of the drum chamber.
 18. The solid-bowl screw centrifuge according to claim 1, wherein a maximal radial dimension of the at least one conical disk is approximately ⅔ of one of a radial space between the screw body and the drum casing and a radial space of the drum chamber.
 19. The solid-bowl screw centrifuge according to claim 1, further including one or more of a flush-back device, a centrifugal valve and a nozzle for cleaning at least a portion of the centrifuge.
 20. The solid-bowl screw centrifuge according to claim 1, further including a regulating disk slidable axially in front of the liquid outlet for regulating a liquid level.
 21. The solid-bowl screw centrifuge according to claim 1, wherein an angle of slope of the at least one conical disk, with respect to a rotational axis of the drum, is between 40° and 50°. 